A common way to form images on media, such as paper, is to use a fluid-ejection device, such as an inkjet-printing device. An inkjet-printing device has a number of inkjet-printing mechanisms, such as inkjet printheads. Each inkjet printhead has a number of inkjet nozzles that eject ink, such as differently colored ink, in such a way as to form a desired image on the media. Many inks are dye-based, but other inks are pigment-based, which are usually more viscous than dye-based inks.
Inkjet printheads can lose water contained within the ink through the inkjet nozzles, as well as through the body of the printheads and the tubing that delivers the ink to the printheads. When too much water is lost from the ink, the viscosity of the ink can increase, and/or the ink suspension can become unstable. Either of these situations can result in poor image formation quality.
Ink can also gain air over time through the tubing that delivers the ink to an inkjet printhead. As this ink is brought into the inkjet printhead, the dissolved air outgases from the ink as the ink is temperature-cycled through usage of the printhead. This air becomes trapped within the housing or body of the inkjet printhead, decreasing the available volume for replenishment of the ink. As a result, poor image formation quality can occur in this situation as well.